Orthogonal frequency division multiplexing (OFDM) is a multi-carrier transmission technique in which a user transmits on many orthogonal frequencies (or subcarriers). The orthogonal subcarriers are individually modulated and separated in frequency such that they do not interfere with one another. This provides high spectral efficiency and resistance to frequency selective fading and multipath effects. An orthogonal frequency division multiple access (OFDMA) system allows some subcarriers to be assigned to different subscriber stations, rather than to a single subscriber station. Today, OFDM and OFDMA technology are used in both wireline transmission systems, such as asymmetric digital subscriber line (ADSL), and wireless transmission systems, such as IEEE-802.11a/g (i.e., WiFi), IEEE-802.16 (e.g., WiMAX), digital audio broadcast (DAB), and digital video broadcast (DVB). This technology is also used for wireless digital audio and video broadcasting.
In some OFDM networks, two primary broadcast channels are used to provide system information, quick page and superframe control information from a base station to subscriber stations. Proposed base station designs assign consecutive subcarriers within two symbols of a superframe preamble to each of the broadcast channels. Because of this, when a subscriber station is in a frequency-selective channel environment, most of the data transmitted in the contiguous subcarriers may be lost when that part of the spectrum is in deep fade. In addition, subscriber stations are required to demodulate the data in both broadcast channels for each superframe, even though the data may remain unchanged. Therefore, there is a need in the art for an improved method for generating a superframe preamble in an OFDM network.